U.S. patent application number 12/562557 was filed with the patent office on 2010-03-25 for lanthanide metal-organic frameworks and uses thereof.
This patent application is currently assigned to University of Pittsburgh--Of the Commonwealth System of Higher Education. Invention is credited to Demetra Anne Chengelis Czegan, Ptephane Petoud, Nathaniel L. Rosi, Kiley A. White.
Application Number | 20100072424 12/562557 |
Document ID | / |
Family ID | 42036697 |
Filed Date | 2010-03-25 |
United States Patent
Application |
20100072424 |
Kind Code |
A1 |
Petoud; Ptephane ; et
al. |
March 25, 2010 |
LANTHANIDE METAL-ORGANIC FRAMEWORKS AND USES THEREOF
Abstract
Metal-organic frameworks (MOFs) are crystalline porous materials
that include metal ions linked together into periodic structures
via organic ligands. MOFs that contain lanthanide ions are a new
class of visible and near-IR luminescent materials, suitable for a
broad range of applications. For example, the MOF framework
afforded by
2,5-dimethoxy-1,4-phenylene)di-2,1-ethenediyl]bis-carboxylate is
associated with unusually long luminescence lifetimes. Thus, a
complex of this ligand with a lanthanide provides a sharp emission
profile, coupled with a comparatively long signal lifetime, for an
unusually high luminescence. More generally, lanthanide-MOF systems
exhibit several advantages that are ideal for barcoded materials,
due to the photophysical attributes of lanthanide cations and the
well-defined organization of the MOF structure.
Inventors: |
Petoud; Ptephane;
(Pittsburgh, PA) ; Rosi; Nathaniel L.;
(Pittsburgh, PA) ; White; Kiley A.; (Pittsburgh,
PA) ; Czegan; Demetra Anne Chengelis; (Greensburg,
PA) |
Correspondence
Address: |
FOLEY AND LARDNER LLP;SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
University of Pittsburgh--Of the
Commonwealth System of Higher Education
|
Family ID: |
42036697 |
Appl. No.: |
12/562557 |
Filed: |
September 18, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61136607 |
Sep 18, 2008 |
|
|
|
Current U.S.
Class: |
252/301.16 ;
534/15 |
Current CPC
Class: |
C09K 2211/1074 20130101;
C09K 2211/1029 20130101; C09K 2211/1088 20130101; C07C 65/28
20130101; C09K 11/06 20130101; C09K 2211/182 20130101; C09K
2211/1011 20130101; C09K 2211/1022 20130101; C09K 2211/1044
20130101; C09K 2211/1007 20130101 |
Class at
Publication: |
252/301.16 ;
534/15 |
International
Class: |
C09K 11/06 20060101
C09K011/06; C07F 5/00 20060101 C07F005/00 |
Claims
1. A composition comprising a lanthanide and an organic ligand that
is complexed to said lanthanide, wherein said ligand has multiple
metal-binding sites and an electronic structure that accommodates
transfer of energy to said lanthanide.
2. A composition according to claim 1, wherein said ligand is
(4,4'-[(2,5-dimethoxy-1,4-phenylene)di-2,1-ethenediyl]bis-carboxylate).
3. A composition according to claim 1 or claim 2, wherein said
ligand is complexed to at least two different lanthanides.
4. A composition according to claim 3, wherein said lanthanides are
selected from the group consisting of erbium, ytterbium, and
neodymium.
5. A composition according to claim 3, wherein said lanthanides are
selected from the group consisting of samarium, holmium, thulium,
praseodymium and dysprosium.
6. A composition according to claim 3, wherein said lanthanides are
selected from the group consisting of europium, terbium, and
gadolinium.
7. A composition according to claim 4, wherein said composition has
the formula
(Er.sub.xYb.sub.y).sub.2(4,4'-[(2,5-dimethoxy-1,4-phenylene)di-2-
,1-ethenediyl]bis-carboxylate).sub.3, where: x is a number between
0 and 1; and y is a number having a value equal to (1-x).
8. A composition according to claim 7, wherein x is 0.81, 0.7,
0.58, or 0.32 and y is 0.19, 0.3, 0.42, or 0.68.
9. A method for marking an object with a metal-organic complex,
comprising: (a) providing a composition comprised of at least one
metal-organic complex that comprises an organic ligand and at least
two different lanthanides, wherein said lanthanides are present in
a predetermined ratio and wherein said ligand has multiple
metal-binding sites and an electronic structure that accommodates
transfer of energy to said lanthanides; and then (b) applying said
composition to said object.
10. A method according to claim 9, wherein said applying comprises
loading a device with said composition and then using said device
to mark said object with said composition.
11. A method of preparing a metal-organic complex, comprising: (a)
providing an organic ligand that binds to a lanthanide, wherein
said ligand has multiple metal-binding sites and an electronic
structure that accommodates transfer of energy to said lanthanide;
(b) reacting said ligand and at least one lanthanide in a reaction
mixture to form a metal-organic complex, such that the distance
between said ligand and said lanthanide in said complex is
controlled; and then (c) crystallizing said complex from said
reaction mixture, forming crystals of said complex.
12. A method according to claim 11, further comprising isolating
said crystals from said reaction mixture.
Description
[0001] This application claims priority from U.S. Provisional
Application No. 61/136,607, filed Sep. 18, 2008, incorporated
herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] New methods for lanthanide sensitization are of great
interest due to the incorporation of lanthanide luminescence in a
portfolio of applications, including photonic materials, liquid
lasers, and telecommunication devices. Near-IR (NIR)-emitting
lanthanides are of particular interest for biological imaging
because of their advantageous electronic properties compared to
that of common organic fluorophores.
[0003] Lanthanide emission bands are sharp, occur at fixed
wavelengths, and are not affected by environmental factors such as
pH or temperature. Accordingly, they are easily detected and
discriminated from background signals. Lanthanide cations also have
long luminescence lifetimes and are highly resistant to
photobleaching, allowing for extended storage time and repeated
exposure to excitation sources.
[0004] Since f-f transitions are Laporte-forbidden, however, free
lanthanide cations have extremely low absorptivity, which limits
their luminescence intensity. To overcome this limitation, an
"antenna effect" has been exploited to improve the efficiency of
lanthanide luminescence. By this approach, lanthanide cations are
complexed with "antennae," i.e., molecules with high absorptivity
that can transfer their absorbed energy to sensitize the lanthanide
cations.
[0005] Different strategies have been applied to sensitize
NIR-emitting Ln, including use of dendrimer and nanocrystalline
forms. The organization of the antennae about the lanthanide cation
significantly impacts the luminescent properties of the complex.
Ideally, lanthanides should be effectively shielded from water
(O--H) vibrations for sufficient luminescence lifetimes and for
discrimination from background signals.
[0006] These challenges are hard to overcome because lanthanide
cations generally exhibit low stereochemical requirements.
Accordingly, it has proven difficult to control the organization of
the ligands in a prescribed manner.
SUMMARY OF THE INVENTION
[0007] The inventors have addressed this problem through a
supramolecular approach, in which the ligand is purposefully
designed to have a coordination environment that meets the
requirements for lanthanide cations. By this approach,
metal-organic framework (MOF) materials are a means not only to
sensitize lanthanides but also to optimize their excitation and
emissive properties.
[0008] MOFs are a relatively new class of porous materials that are
made up of metal ions or clusters, which are linked together into
periodic two or three dimensional lattices via multitopic organic
ligands. The metals and ligands can be chosen to impart specific
function to the MOF.
[0009] Numerous lanthanide-containing MOFs have been synthesized,
and sensing applications based on their visible emission properties
have been exploited. On the other hand, MOFs have not been designed
heretofore to sensitize and optimize the photophysical properties
NIR-emitting lanthanides specifically.
[0010] The present invention exploits certain features of MOFs in
order to improve lanthanide sensitization in the NIR. First, MOFs
can have rigid architectures in which the metals and ligands are
well-organized and constrained in space. Second, MOFs can adopt a
variety of topologies, and in some cases the topological features
of a MOF can be designed in an a priori fashion.
[0011] To date MOFs have been designed for gas storage and
sequestration, catalysis, and separations, among other
applications. The present inventors report a new approach for
generating "barcoded" systems that utilize MOFs, containing
multiple near-infrared (NIR) emitting lanthanides, that are
characterized by well-controlled composition and photophysical
properties. Furthermore, MOFs have well-defined crystalline
structures, which accommodate incorporation of multiple different
cations and organic sensitizers with a high degree of spatial
organization. The crystalline nature of these materials allows for
unambiguous rationalization of the luminescence properties, based
on the specialized structures described here.
[0012] A preferred MOF framework is afforded by
2,5-dimethoxy-1,4-phenylene)di-2,1-ethenediyl]bis-carboxylate, a
ligand associated with unusually long luminescence lifetimes in the
NIR range. Thus, a complex of this ligand with a lanthanide
provides a sharp emission profile in the NIR, coupled with a
comparatively long signal lifetime, for an unusually high
luminescence.
[0013] More generally, the inventors have discovered that
lanthanide-MOF systems exhibit several advantages making them ideal
as barcoded materials, due to the photophysical attributes of
lanthanide cations and the well-defined organization of the MOF
structure. Such systems provide an conclusive way to recognize the
identity of an object or a biological entity. To this end, highly
reproducible, barcoded MOF materials are provided that, in
accordance with the invention, display NIR emissions based on
ratiometric control of lanthanide composition within the MOFs.
[0014] Furthermore, multiple different lanthanide cations can be
incorporated yielding highly reproducible barcoded MOF materials
with NIR emissions based on control of the relative lanthanide
ratios within the MOFs.
[0015] For practical applications, barcoded materials must be
incorporated into objects, e.g. money or an article of clothing, in
ways that do not detrimentally affect their signal. The inventors
have demonstrated barcoded MOF materials, pursuant to the
invention, are characterized by such robustness in marking
usage.
[0016] The inventors also have validated a MOF approach for
generating barcoded materials that is based on the sharp emission
of lanthanide cations. That is, they devised a new system that is
useful for preparing polymetallic lanthanide compounds that
simultaneously emit several independent luminescence signals.
Pursuant to the invention, one can predict and control the
lanthanide composition of the material and, hence, the resulting
emission intensities, by varying the synthetic conditions. For
instance, it is shown that excitation at a single wavelength
produces concurrent ytterbium and erbium emission bands that are
linearly correlated to the lanthanide ratio. In this regard,
Er.sub.xYb.sub.1-x-PVDC-1 MOFs illustrate the properties that
typify barcoded luminescent materials of the invention, which have
a myriad of marking uses for practical application.
[0017] In accordance with one aspect of the invention, therefore, a
composition is provided that comprises a lanthanide and an organic
ligand that is complexed to the lanthanide, where the ligand has
multiple metal-binding sites and an electronic structure that
accommodates transfer of energy to the lanthanide. In a composition
of the invention, the ligand can be complexed to at least two,
three or more different lanthanides, such as erbium, ytterbium, and
neodymium. Exemplary of other, suitable lanthanides are samarium,
holmium, thulium, praseodymium and dysprosium, which also are
NIR-emitting cations, as well as europium, terbium, and
gadolinium.
[0018] In a preferred embodiment, the ligand is
(4,4'-[(2,5-dimethoxy-1,4-phenylene)di-2,1-ethenediyl]bis-carboxylate).
Thus, a composition of the invention can have the formula:
(Er.sub.xYb.sub.y).sub.2(4,4'-[(2,5-dimethoxy-1,4-phenylene)di-2,1-ethen-
ediyl]bis-carboxylate).sub.3,
where x is a number between 0 and 1 and y is a number having a
value equal to (1-x). In such a composition, therefore, x could be
0.81, 0.7, 0.58, or 0.32 and y could be 0.19, 0.3, 0.42, or 0.68,
inter alia.
[0019] According to another aspect, the invention provides a method
for marking an object with a metal-organic complex. The inventive
methodology comprises:
[0020] (a) providing a composition comprised of at least one
metal-organic complex that comprises an organic ligand and at least
two different lanthanides, wherein said lanthanides are present in
a predetermined ratio and wherein said ligand has multiple
metal-binding sites and an electronic structure that accommodates
transfer of energy to said lanthanides; and then
[0021] (b) applying said composition to said object. In such a
method, pursuant to the invention, the applying can comprise
loading a device with said composition and then using said device
to mark said object with said composition.
[0022] In accordance with yet another aspect, a method is provided
for preparing a metal-organic complex. The method comprises: (a)
providing an organic ligand that binds to a lanthanide, wherein
said ligand has multiple metal-binding sites and an electronic
structure that accommodates transfer of energy to said lanthanide;
(b) reacting said ligand and at least one lanthanide in a reaction
mixture to form a metal-organic complex, such that the distance
between said ligand and said lanthanide in said complex is
controlled; and then (c) crystallizing said complex from said
reaction mixture, forming crystals of said complex. In a further
step, the crystals thus formed may be isolated from the reaction
mixture.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 presents structural and spectral data for Yb-PVDC-1.
There are a ball-and-stick depiction of infinite SBU (a) and SBU
with Yb.sup.3+ represented as polyhedra (b) (C, grey; O, red;
Yb.sup.3+, dark green); a projection view of the framework, seen
along the a crystallographic direction (c); a ligand stacking motif
along [110] (d); and luminescent data comparing the excitation
profiles of the Yb-PVDC molecular complex (red; .lamda..sub.em=980
nm) to Yb-PVDC-1 (blue; .lamda..sub.em=980 nm) and displaying the
Yb.sup.3+ emission (green; .lamda..sub.ex=470 nm), collected upon
excitation of Yb-PVDC-1 (e).
[0024] FIG. 2 presents structural and spectral data for Yb-PVDC-2.
There are a ball-and-stick depiction of infinite SBU (a) and SBU
with Yb.sup.3+ represented as polyhedra (b); a projection view of
the framework, seen along the a crystallographic direction (c);
ligand stacking motifs (d) (C, grey; O, red; Yb3+, dark green); and
luminescent data comparing the excitation profiles of Yb-PVDC-1
(red; .lamda..sub.em=980 nm) to Yb-PVDC-2 (blue; .lamda..sub.em=980
nm) and displaying the Yb.sup.3+ emission (green;
.lamda..sub.ex=500 nm), collected upon excitation of Yb-PVDC-2
(e).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] Typically, lanthanides are sensitized by means of small
molecules. In contrast, the present invention sensitizes
lanthanides through the use of MOFs, which characteristically are
porous, crystalline solid-state materials. In accordance with the
invention, MOFs allow the formation of luminescent compounds that
contain a large number of lanthanide cations per unit of volume,
resulting in increased luminescence signal. Thus, MOFs provide a
unique means for effecting better control of ligand (sensitizer)
geometry around the lanthanide metal. Moreover, MOFs provide for
effectively shielding the lanthanide ions from certain solvents
that may quench the luminescence. Lanthanide cations need to be
sensitized by an appropriate antenna, in order to emit an
appropriate signal. Pursuant to the invention, MOFs allow an
improved control of such sensitization through modification of the
excitation wavelength; this, due to the rigidity of the structures
and preorganization of intermolecular interactions to lower the
excitation energy.
[0026] The inventors initially identified a ligand that could both
effectively sensitize the NIR emission of Yb.sup.3+ and promote its
assembly into an extended porous network.
4,4'-[(2,5-dimethyoxy-1,4-phenylene)di-2,1-ethenediyl]bis[benzoic
acid] (H.sub.2-PVDC) was selected because of its strong
absorptivity in the visible, its length, which could promote the
formation of large, accessible pores, and the fact that it was
capable of sensitizing the NIR emission of Yb.sup.3+ (see below).
The inventors chose to target MOFs with infinite Yb-carboxylate
chains or infinite secondary building units (SBUs). Infinite SBUs
force the ligands into parallel packing arrangements and they are
known to promote the formation of non-interpenetrated structures,
regardless of the length of the linker. Several lanthanide-based
MOFs exhibiting infinite SBUs have been constructed previously.
[0027] As described in greater detail below, reacting
Yb(NO.sub.3).sub.3.5H.sub.2O with H.sub.2-PVDC yielded Yb-PVDC-2,
formulated as
Yb.sub.2(C.sub.26H.sub.20O.sub.6).sub.3.(DMF).sub.12(H.sub.2O).sub.10.
Yb-PVDC-2 crystallizes in the orthorhombic Pnna spacegroup, and it
also exhibits infinite Yb-carboxylate SBUs. The SBU is composed of
alternating octa- and hexa-coordinated Yb.sup.3+. The Yb.sup.3+ are
bridged by two carboxylates, in a di-mondodentate fashion, and a
third carboxylate, which chelates the octa-coordinate Yb.sup.3+ and
coordinates in a monodentate fashion to the hexa-coordinate
Yb.sup.3+ (FIG. 1a,b).
[0028] These coordination modes result in a chain of corner-sharing
polyhedral Yb.sup.3+. Each chain is linked to a total of six other
chains via the phenylenevinylene portion of the PVDC linkers. The
ligands that connect the chains along the [001] stack in parallel
with one another, while the ligands that connect the chains in the
[011] form pairs that criss-cross with one another, resulting in
close .pi.-.pi. interactions between the central phenyl rings of
the PVDC linkers (FIG. 1c). Each infinite SBU is connected to six
other SBUs, resulting triangular channels that measure
approximately 13-14 .ANG. from corner to edge.
[0029] In order to determine how the MOF structure affects the
luminescent properties of the Yb-PVDC system, the absorbance,
emission, and excitation of PVDC and the Yb-PDC complex were
measured. (See example below for details on the preparation of
Yb-PVDC.) Due to solubility constraints, it was necessary to use
DMSO as the solvent for these experiments.
[0030] As shown in FIG. 2, the absorbance spectrum of PVDC displays
two bands centered at 340 and 415 nm. Excitation through either of
these bands produces a fluorescence band centered at 485 nm and the
excitation spectrum on this fluorescence band shows a profile
similar to the absorbance spectrum. As illustrated in FIG. 2, the
Yb-PVDC complex displays Yb.sup.3+ emission in the NIR range, with
the typical band maxima of 980 nm. The excitation spectrum of
Yb.sup.3+ emission (FIG. 2) displays two bands, centered at 340 and
415 nm, the same profile as the absorbance of PVDC, indicating that
Yb.sup.3+ is sensitized effectively by PVDC via the antennae
effect.
[0031] Luminescence analysis of MOF Yb-PVDC-1 was performed with a
crystalline MOF sample kept under chloroform. The MOF Yb-PVDC-2
also displayed Yb.sup.3+ luminescence (FIG. 2). In contrast to
Yb.sup.3+ excitation in complex with PVDC in solution, however the
MOF excitation was notably red-shifted, displaying three bands with
maxima at 280, 370, and 510 nm, illustrated in FIG. 2.
[0032] The close .pi.-.pi. interactions between the PVDC in
Yb-PVDC-2 results, it is believed, in a decrease in the
.pi..fwdarw..pi.*. transition of the ligand, thus causing a
decrease in the excitation energy. In accordance with the
invention, therefore, imparting specific ligand-ligand interactions
in the context of a MOF can produce low energy excitation pathways
for NIR antennae.
[0033] The structure of the MOF induces the lowering of the
excitation wavelength, which allows for more sensitive detection in
biological media by decreasing biological fluorescence background.
This is so because naturally occurring molecules tend to have an
excitation wavelength, located higher in energy.
[0034] One application for these NIR-emitting MOFs is as
bio-imaging reagents. The size of the MOF could be controlled via
the addition of surfactant during synthesis, thus creating
nano-scale MOFs. The nano-scale MOFs could be coated into a silica
bead, which then could be functionalized to impart biocompatibility
and recognition abilities.
[0035] For Yb-PVDC-1, it was possible to excite ytterbium emission
at wavelengths up to .about.510 nm; and for Yb-PVDC-2, wavelengths
of up to .about.540 nm were achieved. These are much lower in
energy than the wavelengths possible for the complexes formed with
Yb.sup.3+ and H.sub.2-PVDC, which gives the MOFs a major advantage
that is impossible to be obtained with organic fluorophores or with
semiconductor nanocrystals (quantum dots). It is likely the MOF
structure improves the rigidity of the aromatic chromophoric
groups, thus lowering the electronic energy states of the
chromophoric groups. It also is feasible, as demonstrated through
Yb-PVDC-2, to achieve structural arrangements with close .pi.-.pi.
interactions, further lowering the energy necessary for
sensitization while at the same time improving the efficiency.
[0036] Lower excitation energy has two main benefits for a
bio-imaging application. First, there are many naturally occurring
luminescent species in biological media, most of which are excited
in the ultra-violet to blue range [200-375 nm]. The native
fluorescence background often is referred to as "autofluorescence."
Most conventional bio-imaging reagents also are excited in this
range, and their fluorescence is difficult to distinguish from the
autofluorescence, thus reducing sensitivity. Furthermore, since
much of the incident excitation light is absorbed by the biological
media in addition to the imaging reagent, more intense excitation
source is necessary to achieve sufficient absorption for detectable
fluorescence. Shifting excitation wavelengths to 500 nm
significantly reduces the amount of autofluorescence generated by
biological media, thus the luminescence of the MOFs could be
detected with improved sensitivity using a less intense excitation
source.
[0037] Secondly, it would be ideal to achieve excitation at
wavelengths in the NIR window, >640 nm. In this range, light can
deeply penetrate through biological tissue such as skin and blood,
allowing for in vivo applications. With the invention, it is
demonstrated that the excitation wavelengths can be red-shifted
through appropriately designed MOFs. By choosing a different
chromophoric group with lower energy absorption than H.sub.2PVDC,
it should be possible to use the MOF strategy to achieve excitation
at the desired 640 nm or higher wavelength.
[0038] In this description, the term "object" denotes an article of
manufacture including but not limited to parcels, mechanical parts,
biological samples, electronic chip cards, check cards, credit
cards, identity cards, bank notes, certificates, documents and the
like.
[0039] The term "composition" denotes one or more lanthanides bound
or coordinated to an organic compound capable of binding to a
lanthanide, and additionally including water and/or organic
solvent.
[0040] The term "device" here refers to a printing system, stamp,
rollerball pen, fountain pen, felt-tip pen, dip pen, paint brush,
ink jet printer, spinneret, clear tube or similar small clear
container and the like.
[0041] In the present context, the term "ligand" denotes any
organic compound that: (A) binds to a lanthanide; (B) has multiple
metal-binding sites and, hence, is capable of binding more than one
type of lanthanide, if desired; and (C) an electronic structure
that accommodates transfer of energy from the ligand to a complexed
lanthanide, sensitizing the latter, e.g., via electron transfer, a
Dexter Mechanism, or a dipole-dipole interaction. Illustrative of
this category are ligands that are substituted triphenylene
compounds, substituted pyrenes, fluorescein anions, eosin anions,
erythrosine anions, fluorexon anions, substituted poly(pyrazole)
borates, substituted podate anions, Lehn cryptands, porphyrins,
1,3-diketonates, pyridines, polypyridines and related derivatives,
dipicolinates and related derivatives, hydroxyquinolines and
related derivatives, and
(4,4'-[(2,5-dimethoxy-1,4-phenylene)di-2,1-ethenediyl]bis-carboxylate).
[0042] The phrase "predetermined ratio" denotes the relative ratios
of multiple near-infrared (NIR) emitting lanthanides, that are
characterized by well-controlled composition and photophysical
properties. Specifically, the ratio of different lanthanides
control the characterization of the photophysical properties as to
afford a signal that is employed to distinguish one marked object
from each other. Objects marked with multiple different,
NIR-emitting lanthanide compositions containing different ratios of
different lanthanides can be distinguished spectroscopically.
[0043] The terms "mark" and "marked" denote the result of applying
a composition of the invention to an object.
[0044] In this regard, "crystallizing" refers to a process or
separation technique in which solute from the liquid solution is
precipitated in a crystalline phase.
[0045] The term "isolating" here means that when isolated (e.g.,
from other components of a synthetic chemical reaction mixture),
the isolate contains at least 30%, at least 35%, at least 40%, at
least 45%, at least 50%, at least 55%, at least 60%, at least 65%,
at least 70%, at least 75%, at least 80%, at least 85%, at least
90%, at least 95% or at least 98% of an Lanthanide Compound by
weight of the isolate. In one embodiment, the isolate contains at
least 95% of an Lanthanide Compound by weight of the isolate.
[0046] The invention is described further below, by reference to
the following examples, which are illustrative only.
EXAMPLE I
Phenylene Derivative Barcoded Metal Organic Frameworks Containing
Varied Yb.sup.3+ and Er.sup.3+ Stoichiometries
[0047] Two illustrative, Yb.sup.3+-based MOFs, Yb-PVDC-1 and
Yb-PVDC-2, can be tuned and optimized in relation to the
photophysical properties of Yb.sup.3+ by tailoring MOF
architecture. In addition, these materials have long luminescence
lifetimes and high quantum yields compared to other Yb.sup.3+-based
systems under solvent.
[0048] The synthesis of Yb-PVDC-1 can be modified in accordance
with the invention to yield barcoded frameworks containing both
ytterbium and erbium. Yb.sup.3+ and Er.sup.3+ were chosen because
they have very distinct emission profiles in the NIR. Specifically,
we reacted
(4,4'-[(2,5-dimethoxy-1,4-phenylene)di-2,1-ethenediyl]bis-benzoic
acid), our chosen antenna, with Er(NO.sub.3).sub.3.5H.sub.2O and
Yb(NO.sub.3).sub.3.5H.sub.2O to produce yellow needles of four
luminescent frameworks with varying lanthanide metal
stoichiometries: (1) Er.sub.0.32Yb.sub.0.68-PVDC-1; (2)
Er.sub.0.58Yb.sub.0.42-PVDC-1; (3) Er.sub.0.70Yb.sub.0.30-PVDC-1;
and (4) Er.sub.0.81Yb.sub.0.19-PVDC-1.
EXAMPLE II
Phenylene Derivative Metal Organic Framework as Scaffold Antenna
for Yb.sup.3+
[0049] Two MOF structures are presented, both using Yb.sup.3+ and a
phenylene derivative organic chromophoric group. This ligand has
not been used previously for the synthesis of MOFs, and its
structure, as well as the structure of the resulting MOF complex,
has not been described heretofore.
[0050] These two MOFs, Yb-PVDC-1 and Yb-PVDC-2, demonstrate that
utilizing the MOF structural backbone in combination with
NIR-emitting lanthanide cations, in accordance with the invention,
results in a novel type of NIR-emitting material with superior
luminescence properties: quantum yields values among the highest
reported in the literature and these MOFs have longer luminescence
lifetimes, i.e., more than twice the value observed for comparable
NIR-emitting lanthanide complexes. These superiorities in
luminescence quantum yields, and lifetimes will result in a
significant increase in detection sensitivity. Such advantage
cannot be obtained with organic fluorophores, semiconductor
nanocrystals, or "non-MOFS" lanthanide complexes.
I. Synthesis and Characterization
[0051] Initially, the inventors identified a ligand that could both
sensitize NIR-emitting Yb.sup.3+ and direct its assembly into an
extended porous network.
4,4'-[(2,5-dimethoxy-1,4-phenylene)di-2,1-ethenediyl]bis-benzoic
acid (H.sub.2-PVDC) was chosen because it has strong absorptivity
in the visible range because it could promote the formation
extended MOF structures, and because preliminary studies indicated
that it was capable of sensitizing NIR-emitting Yb.sup.3+ (see
below).
A. Synthesis of H.sub.2-PVDC
1,4-Bis(bromomethyl)-2,5-dimethoxybenzene (1)
##STR00001##
[0053] This intermediate was prepared following Zhang et al.,
Angew. Chem., 117: 2564 (2005); Angew Chem. Int'l Ed. 44: 2508
(2005), as detailed here. To a stirred solution of
1,4-dimethoxybenzene (Aldrich, 10.00 g, 72.37 mmol) in glacial
acetic acid (Fisher, 50 mL), paraformaldehyde (Aldrich, 4.27 g,
144.75 mmol) and HBr/AcOH (Fluka, 33%, 30 mL) were added slowly.
The mixture was stirred at 50.degree. C. for one hour and
hydrolyzed in water (200 mL) after cooling to room temperature. The
white solid was collected by filtration, suspended in CHCl.sub.3
(50 mL), and refluxed for 10 min. After cooling to room
temperature, the white solid was again collected by filtration and
washed with water (15.75 g, 67%). .sup.1H NMR (300 MHz, CDCl.sub.3)
.delta. 6.88 (s, 2H), 4.54 (s, 4H), 3.87 (s, 6H) ppm; .sup.13C NMR
(75 MHz, CDCl.sub.3) .delta. 151.9, 128.0, 114.5, 56.9, 29.1 ppm;
FTIR (KBr pellet): 2962 (w), 2934 (w), 2834 (w), 1509 (vs), 1461
(s), 1428 (w), 1404 (vs), 1319 (m), 1228 (vs), 1205 (s), 1179 (w),
1103 (w), 890 (w), 874 (w), 718 (w) cm.sup.-1. HRMS (EI.sup.+)
Calcd for C.sub.10H.sub.12O.sub.2Br.sub.2 [M].sup.+321.9204, found
321.9209.
2,5-Dimethoxy-1,4-phenylene)bis(methylene)bis(triphenylphosphonium
bromide (2)
##STR00002##
[0055] A mixture of 1,4-bis(bromomethyl)-2,5-dimethoxybenzene 1
(9.59 g, 29.60 mmol) and triphenylphosphine (Aldrich, 18.63 g,
71.04 mmol) was refluxed in dry toluene (Acros, 99.8%, 80 mL) under
argon for 6 hours. The crude white powder was obtained by
filtration and used for subsequent reaction without further
purification.
Dimethyl
4,4'-(1E,1'E)-2,2'-(2,5-dimethoxy-1,4-phenylene)bis(ethane-2,1-di-
yl)dibenzoate (3)
##STR00003##
[0057] The following procedure was adapted from Stammel et al.,
Eur. J. Org. Chem. (1999), 1709. A mixture of
(2,5-dimethoxy-1,4-phenylene)bis(methylene)bis
(triphenylphosphonium bromide) 2 (25.68 g, 30.26 mmol) and methyl
4-formylbenzoate (TCI, 12.42 g, 75.66 mmol) was dissolved in dry
methanol (Aldrich, 99.8%, 120 mL) under argon. NaOMe (Aldrich, 0.5
M in methanol, 160 mL) was added via cannula. A yellow precipitate
formed immediately. The reaction was stirred under argon for 4
hours. After addition of water (140 mL), the yellow powder was
filtered and washed with aqueous ethanol (60%, 3.times.75 mL). Pure
trans product was isolated via crystallization from toluene in the
presence of few crystals of iodine (11.95 g, 86%) .sup.1H NMR (300
MHz, CHCl.sub.3) .delta. 8.02 (d, J=8.7, 4H), 7.59 (m, 6H), 7.16
(m, 4H), 3.95 (s, 6H), 3.93 ppm (s, 6H); .sup.13C NMR (75 MHz,
CHCl.sub.3) .delta.167.5, 152.4, 142.9, 130.6, 129.4, 128.8, 127.2,
127.0, 126.3, 109.9, 56.9, 52.66 ppm; FTIR (KBr pellet): 3007 (w),
2943 (w), 2835 (w), 1714 (vs), 1604 (m), 1493 (w), 1464 (w), 1437
(sh), 1410 (m), 1277 (vs), 1209 (s), 1183 (m), 1111 (s), 1041 (m),
1014 (w), 971 (trans=C--H, w), 875 (sh), 849 (w), 766 (m), 702
cm.sup.-1 (w). HRMS (EI+) Calcd for C.sub.28.sup.14.sub.26O.sub.6
[M].sup.+458.1729, found 458.1727
4,4'-(1E,1'E)-2,2'-(2,5-dimethoxy-1,4-phenylene)bis(ethene-2,1-diyl)dibenz-
oic acid (4)
##STR00004##
[0059] To dimethyl
4,4'-(1E,1'E)-2,2'-(2,5-dimethoxy-1,4-phenylene)bis(ethane-2,1-diyl)diben-
zoate (5.46 g, 11.9 mmol) was added KOH (Alfa Aesar, 6.2 g, 121
mmol), methanol (60 mL), THF (60 mL), and H.sub.2O (30 mL). The
mixture was refluxed overnight, cooled, and H.sub.2O (60 mL) was
added, resulting in a clear yellow solution. The solution was
acidified with 2N HCl and the resulting yellow solid was collected
by filtration and was then recrystallized from DMF to yield a
bright yellow powder (4.24 g, 83%). .sup.1H NMR (300 MHz, DMSO)
.delta. 12.87 (s, 2H), 7.95 (d, J=7.5, 4H), 7.70 (d, J=8.4, 4H),
7.51 (d, J=21.9, 2H), 7.45 (d, J=15.9, 2H), 7.39 (s, 2H), 3.93 ppm
(s, 6H); .sup.13C NMR (75 MHz, DMSO) .delta. 168.14, 152.30,
142.64, 130.94, 130.43, 129.33, 127.45, 126.94, 126.01, 110.59,
57.27 ppm; FTIR (KBr pellet): 2938 (b), 2831 (b), 2543 (m), 2361
(w), 1680 (C.dbd.O, s), 1600 (s), 1536 (w), 1491 (w), 1462 (m),
1315 (m), 1290 (s), 1209 (m), 1045 (m), 959 (trans=C--H, w), 859
(w), 771 cm.sup.-1 (w). HRMS (EI+) Calcd for
C.sub.26H.sub.22O.sub.6 [M].sup.+ 430.1416, found 430.1401
B. Synthesis of Yb-PVDC-1 and Yb-PVDC-2
(i) Synthesis of Yb-PVDC-1:
Yb.sub.2(C.sub.26H.sub.20O.sub.6).sub.3(H.sub.2O).sub.2.(DMF).sub.6(H.sub-
.2O).sub.8.5
[0060] In a glass vial (4 mL), a solution of
4,4'-(1E,1'E)-2,2'-(2,5-dimethoxy-1,4-phenylene)bis(ethene-2,1-diyl)diben-
zoic acid (H.sub.2-PVDC) (8.60 mg, 0.020 mmol) in DMF (0.4 mL) was
added to a solution of Yb(NO.sub.3).sub.3.5H.sub.2O (6.75 mg, 0.015
mmol) and 1M HNO.sub.3(aq) (20.0 .mu.L) in DMF (0.3 mL) to produce
a neon green solution. The vial was capped and placed in an
85.degree. C. isotemp oven for 48 hours to produce yellow
crystalline needles of the product. The crystals were collected,
washed with DMF (4.times.3 mL), and air dried (8.6 mg, 42.4%).
[0061] EA Calcd. (%) for
Yb.sub.2(C.sub.26H.sub.20O.sub.6).sub.3(H.sub.2O).sub.2.(DMF).sub.6(H.sub-
.2O).sub.8.5: C, 51.04; H, 5.49; N, 3.72. Found: C, 50.97; H, 4.57;
N, 3.91. EA. Calcd. (%) for the chloroform exchange product,
Yb.sub.2(C.sub.26H.sub.20O.sub.6).sub.3(H.sub.2O).sub.2.(CHCl.sub.3).sub.-
2.75(DMF).sub.0.3: C, 48.61; H, 3.44; N, 0.21. Found: C, 48.79; H,
3.10; N, 0.21. FT-IR (KBr 4000-700 cm.sup.-1): 3432 (br), 2933 (w),
1665 (DMF C.dbd.O, m), 1600 (m), 1538 (s), 1414 (COO.sup.-, vs),
1256 (w), 1209 (s), 1180 (w), 1106 (w), 1042 (s), 962 (m), 861 (w),
780 (trans C.dbd.C--H, s), 709 cm.sup.-1(w).
(ii) Synthesis of Yb-PVDC-2: Yb2(C26H20O6)3.(DMF)12(H2O)10
[0062] In a glass vial (20 mL), a solution of
4,4'-(1E,1'E)-2,2'-(2,5-dimethoxy-1,4-phenylene)bis(ethene-2,1-diyl)diben-
zoic acid (H.sub.2-PVDC) (86.0 mg, 0.20 mmol) in DMF (4 mL) was
added to a solution of Yb(NO.sub.3).sub.3.5H.sub.2O (22.5 mg, 0.05
mmol) and 1M HNO.sub.3(aq) (10 .mu.L) in DMF (1 mL) to yield a neon
green solution. The vial was capped and placed in an 105.degree. C.
isotemp oven for 36 hours to produce orange block-like crystals of
the product. The crystals were collected, washed with DMF
(4.times.5 mL) and air dried (48 mg, 51.9%).
[0063] EA Calcd. (%) for
Yb.sub.2(C.sub.26H.sub.20O.sub.6).sub.3.(DMF).sub.12(H.sub.2O).sub.10:
C, 50.93; H, 6.15; N, 6.25. Found: C, 50.95; H, 5.40; N, 6.47. EA.
Calcd. (%) for the chloroform exchange product,
Yb.sub.2(C.sub.26H.sub.20O.sub.6).sub.3.(CHCl.sub.3).sub.7.5(H.sub.2O).su-
b.0.5(DMF).sub.0. 5: C, 40.62; H, 2.82; N, 0.27. Found: C, 40.66;
H, 2.75; N, 0.23. FT-IR (KBr 4000-700 cm.sup.-1): 3433 (br), 2930
(w), 1655 (DMF C.dbd.O, m), 1602 (s), 1536 (m), 1418 (COO.sup.-,
vs), 1208 (s), 1180 (w), 1103 (w), 1041 (w), 960 (trans=C--H, w),
862 (w), 780 cm.sup.-1 (m).
[0064] The molecular formulas for the as-synthesized and
chloroform-exchanged materials were determined through analysis of
the X-ray crystal data and elemental analysis data. While the
absolute framework composition is unambiguous, it is more difficult
to obtain accurate estimations of the quantity of guest molecules
within the pores. This problem is exacerbated by the fact that
these materials have very large cavities which easily lose guest
molecules upon standing. Therefore, it is difficult to directly
compare the number of estimated guest molecules determined form EA
and TGA. These reported formulas are the best possible match to the
EA data.
[0065] Reacting Yb(NO.sub.3).sub.3.5H.sub.2O with H.sub.2-PVDC
yielded yellow needles of Yb-PVDC-1, formulated as
[Yb.sub.2(C.sub.26H.sub.20O.sub.6).sub.3(H.sub.2O).sub.2].(DMF).sub.6(H.s-
ub.2O).sub.8.5. The materials maintain crystallinity in a variety
of solvents, including chloroform and dimethylformamide, as
confirmed by complete solvent exchange experiments and powder X-ray
diffraction studies.
[0066] Single crystal X-ray diffraction analysis revealed that
Yb-PVDC-1 crystallizes in the high symmetry Fddd space group and is
composed of infinite Yb-carboxylate chains that run along the a
crystallographic direction (FIG. 1a-c). The chains consist of
alternating octa- and hexa-coordinated Yb.sup.3+, bridged together
in a di-monodentate fashion via the carboxylates of three different
PVDC linkers (FIG. 1a,b). Two water molecules are terminally
coordinated to the octa-coordinate Yb.sup.3+. These chains are
connected along the [100] via the phenylene vinylene portion of the
ligand resulting in the formation of large rhombus-shaped channels
measuring approximately 24.times.40 .ANG. (FIG. 1c).
[0067] Reacting Yb(NO.sub.3).sub.3.5H.sub.2O with H.sub.2-PVDC
yielded yellow needles of Yb-PVDC-1, formulated as
[Yb.sub.2(C.sub.26H.sub.20O.sub.6).sub.3(H.sub.2O).sub.2].(DMF).sub.6(H.s-
ub.2O).sub.8.5. The materials maintain crystallinity in a variety
of solvents, including chloroform and dimethylformamide, as
confirmed by complete solvent exchange experiments and powder X-ray
diffraction studies.
[0068] Single crystal X-ray diffraction analysis revealed that
Yb-PVDC-1 crystallizes in the high symmetry Fddd space group and is
composed of infinite Yb-carboxylate chains that run along the a
crystallographic direction (FIG. 1a-c). The chains consist of
alternating octa- and hexa-coordinated Yb.sup.3+, bridged together
in a di-monodentate fashion via the carboxylates of three different
PVDC linkers (FIG. 1a,b). Two water molecules are terminally
coordinated to the octa-coordinate Yb.sup.3+. These chains are
connected along the via the phenylene vinylene portion of the
ligand resulting in the formation of large rhombus-shaped channels
measuring approximately 24.times.40 .ANG. (FIG. 1c).
[0069] The UV-Visible absorbance, emission, and excitation spectra
were measured for Yb-PVDC-1 and compared to corresponding spectra
for H.sub.2-PVDC and an Yb-PVDC molecular complex (see supporting
information) to determine how the MOF structure impacts the
luminescence properties of the system. The absorbance spectrum of
H.sub.2-PVDC displays two bands with apparent maxima centered at
340 and 415 nm. Excitation through either of these bands produces a
fluorescence band centered at 485 nm.
[0070] The excitation spectrum recorded upon this fluorescence band
shows a profile similar to the absorbance spectrum. The Yb-PVDC
molecular complex displays Yb.sup.3+ emission in the NIR range,
with a typical apparent maximum of the band at 980 nm. The
excitation spectrum for the complex collected upon monitoring
Yb.sup.3+ emission (FIG. 1e) also contains two bands, centered at
340 and 415 nm, which adopt the same profile as the absorbance of
H.sub.2-PVDC, indicating that PVDC effectively sensitizes Yb.sup.3+
via the antennae effect.
[0071] Luminescence analysis of crystalline Yb-PVDC-1
(chloroformexchanged material) displays Yb.sup.3+ luminescence in
the NIR (FIG. 1e). The MOF excitation spectrum is notably
red-shifted, displaying bands with maxima at 370 and 470 nm (FIG.
1e). The apparent maximum of the excitation band shifts from 415 nm
for the Yb-PVDC complex to 470 nm for Yb-PVDC-1, which is a
significant change.
[0072] Although the Yb-PVDC complex experiments were performed in
DMSO due to solubility constraints, this observed shift over 50 nm
can not solely be attributed to solvatochromic effects. Rather, the
inventors attribute a significant component of this shift to
organizational constraints the MOF architecture imparts on the
phenylene vinylene linkers. In Yb-PVDC-1, the ligands are arranged
in parallel along [110], which may allow for weak interactions
between neighboring ligands (FIG. 1d). These interactions are
hypothesized to affect the electronic structure of the chromophore,
resulting in a decrease of the excitation energy of the
antennae.
[0073] To evaluate the extent to which ligand-ligand interactions
impact the excitation and emission properties of Yb-PVDC systems,
we prepared a second MOF, Yb-PVDC-2, formulated as
[Yb.sub.2(C.sub.26H.sub.20O.sub.6).sub.3].(DMF).sub.12(H.sub.2O).sub.10.
Yb-PVDC-2 crystallizes in the orthorhombic Pnna space group and
also exhibits infinite Yb-carboxylate SBUs. However, the
connectivity within the SBU differs from that of Yb-PVDC-1. The SBU
is composed of alternating octa- and hexa-coordinated Yb.sup.3+.
The Yb.sup.3+ are bridged by two carboxylates in a di-mondodentate
fashion and by a third carboxylate that chelates the
octa-coordinate Yb.sup.3+ and coordinates in a monodentate fashion
to the hexa-coordinate Yb.sup.3+ (FIG. 2a,b). These coordination
modes result in a chain of cornersharing polyhedral Yb.sup.3+. Each
chain is linked to six other chains via the phenylene vinylene
portion of the PVDC linkers (FIG. 2c). The linkers connecting the
chains along the [001] stack in parallel, while those that connect
the chains in the [011] form criss-crossing pairs with close
.pi.-.pi. interactions (3-3.5 .ANG.) between the central phenyl
rings of the PVDC linkers (FIG. 2d). Because each infinite SBU is
connected to six other SBUs, the resulting triangular channels are
smaller than those observed for Yb-PVDC-1, measuring .about.13-14
.ANG. from corner to edge (FIG. 2c).
[0074] The close .pi.-.pi. interactions prompted an examination of
the luminescent properties of Yb-PVDC-2 (chloroform-exchanged
material) to determine whether these interactions impact the
photophysical properties of this system. The excitation spectrum
collected upon monitoring the emission intensity of Yb.sup.3+
luminescence at 980 nm displayed band maxima at 370 and 500 nm
(FIG. 2e). The emission spectra collected in the NIR range upon
excitation at these wavelengths produce characteristic Yb.sup.3+
emission. Interestingly, the lowest energy excitation band of
Yb-PVDC-2 is red-shifted from 470 nm in Yb-PVDC-1 to 500 nm. The
close .pi.-.pi. interactions between the PVDC linkers may decrease
the .pi..fwdarw..pi.* transition, resulting in a lowered excitation
energy.
[0075] In addition to lower energy excitation, the quantum yield of
Yb-PVDC-2, 1.8%, is among the highest values reported for Yb.sup.3+
complexes. In addition to the benefits of lower energy excitation,
as discussed above, the high quantum yield of these MOFs will
further improve detection sensitivity for bioanalytical bio-imaging
applications.
[0076] To determine whether the MOF architecture provides efficient
protection for the lanthanide cations from solvent quenching and to
quantify the intramolecular energy transfer of the systems, quantum
yield values were measured (see Table 1), using an integration
sphere. The quantum yield of Yb-PVDC-2 is five times higher than
Yb-PVDC-1 when excited through the lower energy band (490 nm),
indicating the improved efficiency of the .pi.-.pi.* transition for
intramolecular energy transfer. The quantum yield of Yb-PVDC-2 is
among the highest values reported so far for ytterbium systems
under solvent. These quantum yields are global: the excitation is
performed through the sensitizer and the emission is observed
through the Yb.sup.3+ cations that have two different coordination
environments and levels of protection in both MOFs. In Yb-PVDC-1,
the octa-coordinate Yb.sup.3+ are coordinated by two water
molecules which quench ytterbium emission and lower the global
quantum yield.
[0077] The inventors monitored ytterbium-centered luminescence
lifetimes in order further to determine the effectiveness of the
MOFs in protecting the lanthanide cations from nonradiative
deactivation. Both MOFs displayed multiexponential decay patterns
and were best fit with four components (Table 1), which are
tentatively attributed to four different lanthanide environments:
the hexa-coordinate and octa-coordinate Yb.sup.3+ sites within the
core of the MOF structures and those along the terminating edges of
the crystals, where the lanthanide cations are more exposed to
sources of non-radiative deactivation.
TABLE-US-00001 TABLE 1 ABSOLUTE EMISSION QUANTUM YIELDS
(.PHI.).sup.a AND LUMINESCENT LIFETIMES (.tau..sub.x, .mu.s).sup.b
OF Yb.sup.3+ CENTERED EMISSION AT 980 NM FOR THE MOFs.sup.c
.PHI..sub.Yb.sup.d .tau..sub.1.sup.d .tau..sub.2 .tau..sub.3
.tau..sub.4 Yb-PVDC-1 3.3 (.+-.0.5) .times. 10.sup.-3 29 (.+-.2) 10
(.+-.1) 1.5 (.+-.0.5) 0.34 (.+-.0.06) Yb-PVDC-2 1.8 (.+-.0.2)
.times. 10.sup.-2 22 (.+-.4) 5.6 (.+-.1.5) 1.7 (.+-.0.3) 0.61
(.+-.0.17) .sup.a.lamda..sub.ex = 490 nm. .sup.b.lamda..sub.ex =
354 nm. .sup.cMOFs as crystalline solids under chloroform.
.sup.dError included in parentheses.
[0078] The long component values are up to two times longer than
the longest lifetimes reported for Yb.sup.3+ molecular species in
solution (see Section II, below). These luminescence lifetimes
demonstrate that MOFs can provide coordination environments with
better protection from quenching than molecular complexes.
[0079] Thus, it is illustrated that a MOF-based approach to
sensitize NIR-emitting lanthanides results in materials with
enhanced luminescence properties. Specifically, we have shown that
chromophoric antennae molecules and NIR-emitting lanthanides can be
assembled into rigid MOF structures that effectively control the
coordination environments around the lanthanide cations and the
arrangement of chromophoric antennae. Using this strategy, it was
possible to obtain a lower energy excitation wavelength by
modifying the 3-D MOF structure to allow for close .pi.-.pi.
interactions between the chromophores. The intrinsic structures of
the MOFs provide protection of the lanthanide cations from solvent
vibrations. Finally, MOFs constitute rigid and organized
polymetallic systems with high densities of sensitizing groups and
lanthanide cations per unit of volume for enhanced emission
intensity.
[0080] The Yb-centered luminescence lifetimes for Yb-PVDC-1 and
Yb-PVDC-2 have been measured discussed above. The MOFs display
multi-exponential lifetimes, with the longest values ranging from
22 .mu.s to 29 .mu.s. These lifetimes are significantly longer than
those reported for other Yb.sup.3+ complexes in solution (see
Tables 2-9). The long luminescence lifetimes will improve the
sensitivity of time-resolved measurements due to increases in the
length of time that the signal can be integrated over. In addition,
the electronics and timing circuitry necessary to achieve
time-resolved measurements can be simplified for emitters with
longer lifetimes, thereby decreasing instrumentation costs.
C. Synthesis of (1) Er.sub.0.32Yb.sub.0.68-PVDC-1; (2)
Er.sub.0.58Yb.sub.0.42-PVDC-1; (3) Er.sub.0.70Yb.sub.0.30-PVDC-1;
and (4) Er.sub.0.81Yb.sub.0.19-PVDC-1
(i) Synthesis of (1) Er.sub.0.32Yb.sub.0.68-PVDC-1 (1)
[0081] In a glass vial (4 mL), a solution of
4,4'-(1E,1'E)-2,2'-(2,5-dimethoxy-1,4-phenylene)bis(ethene-2,1-diyl)diben-
zoic acid (H.sub.2-PVDC).sup.1 (8.60 mg, 0.020 mmol) in DMF (0.4
mL) was added to a solution of Yb(NO.sub.3).sub.3.5H.sub.2O (1.02
mg, 0.0025 mmol) in DMF (0.050 mL), Er(NO.sub.3).sub.3.5H.sub.2O
(0.55 mg, 0.00125 mmol) in DMF (0.025 mL), and 1M HNO.sub.3(aq)
(10.0 .mu.L) to produce a neon green solution. The vial was capped
and placed in a 100.degree. C. isotemp oven for 72 hours to produce
yellow crystalline needles. The crystals were collected, washed
with DMF (4.times.3 mL), and air dried (2.1 mg, 52.8%).
[0082] EA Calcd. (%) for
(Er.sub.0.32Yb.sub.0.68).sub.2(C.sub.26H.sub.20O.sub.6).sub.3(H.sub.2O).s-
ub.2.(DMF).sub.5(H.sub.2O).sub.5: C, 52.71; H, 5.18; N, 3.30.
Found: C, 52.79; H, 4.33; N, 2.94. FT-IR (KBr 4000-700 cm.sup.-1):
3381 (br), 2933 (w), 1659 (DMF C.dbd.O, m), 1600 (s), 1536 (s),
1413 (COO.sup.-, vs), 1258 (w), 1209 (s), 1180 (m), 1105 (w), 1042
(s), 962 (m), 865 (w), 780 (trans C.dbd.C--H, s), 709
cm.sup.-1(w).
(ii) Synthesis of (2) Er.sub.0.58Yb.sub.0.42-PVDC-1 (2)
[0083] In a glass vial (4 mL), a solution of
4,4'-(1E,1'E)-2,2'-(2,5-dimethoxy-1,4-phenylene)bis(ethene-2,1-diyl)diben-
zoic acid (H.sub.2-PVDC) (8.60 mg, 0.020 mmol) in DMF (0.4 mL) was
added to a solution of Yb(NO.sub.3).sub.3.5H.sub.2O (1.02 mg,
0.0025 mmol) in DMF (0.050 mL), Er(NO.sub.3).sub.3.5H.sub.2O (1.66
mg, 0.00375 mmol) in DMF (0.075 mL), and 1M HNO.sub.3(aq) (10.0
.mu.L) to produce a neon green solution. The vial was capped and
placed in a 100.degree. C. isotemp oven for 72 hours to produce
yellow crystalline needles. The crystals were collected, washed
with DMF (4.times.3 mL), and air dried (4.6 mg, 31.4%).
[0084] EA Calcd. (%) for
(Er.sub.0.58Yb.sub.0.42).sub.2(C.sub.26H.sub.20O.sub.6).sub.3(H.sub.2O).s-
ub.2.(DMF).sub.8.5(H.sub.2O).sub.5: C, 52.41; H, 5.67; N, 5.02.
Found: C, 52.50; H, 4.87; N, 4.45. FT-IR (KBr 4000-700 cm.sup.-1):
3433 (br), 2934 (w), 1658 (DMF C.dbd.O, m), 1602 (s), 1534 (s),
1418 (COO.sup.-, vs), 1256 (w), 1210 (s), 1181 (w), 1106 (w), 1043
(s), 963 (m), 866 (w), 781 (trans C.dbd.C--H, s), 709
cm.sup.-1(w).
(iii) Synthesis of Er.sub.0.70 Yb.sub.0.30-PVDC-1 (3)
[0085] In a glass vial (4 mL), a solution of
4,4'-(1E,1'E)-2,2'-(2,5-dimethoxy-1,4-phenylene)bis(ethene-2,1-diyl)diben-
zoic acid (H.sub.2-PVDC) (8.60 mg, 0.020 mmol) in DMF (0.4 mL) was
added to a solution of Yb(NO.sub.3).sub.3.5H.sub.2O (1.02 mg,
0.0025 mmol) in DMF (0.050 mL), Er(NO.sub.3).sub.3.5H.sub.2O (2.77
mg, 0.00625 mmol) in DMF (0.125 mL), and 1M HNO.sub.3(aq) (10.0
.mu.L) to produce a neon green solution. The vial was capped and
placed in a 100.degree. C. isotemp oven for 72 hours to produce
yellow crystalline needles. The crystals were collected, washed
with DMF (4.times.3 mL), and air dried (2.3 mg, 9.9%)
[0086] EA Calcd. (%) for
(Er.sub.0.70Yb.sub.0.30).sub.2(C.sub.26H.sub.20O.sub.6).sub.3(H.sub.2O).s-
ub.2.(DMF).sub.12(H.sub.2O).sub.7: C, 51.43; H, 6.13; N, 6.31.
Found: C, 51.42; H, 5.51; N, 6.65. FT-IR (KBr 4000-700 cm.sup.-1):
3436 (br), 2935 (w), 1656 (DMF C.dbd.O, m), 1602 (s), 1542 (s),
1411 (COO.sup.-, vs), 1259 (w), 1209 (s), 1180 (w), 1104 (w), 1043
(s), 947 (m), 865 (w), 780 (trans C.dbd.C--H, s), 709
cm.sup.-1(w).
(iv) Synthesis of Er.sub.0.81Yb.sub.0.19-PVDC-1 (4)
[0087] In a glass vial (4 mL), a solution of
4,4'-(1E,1'E)-2,2'-(2,5-dimethoxy-1,4-phenylene)bis(ethene-2,1-diyl)diben-
zoic acid (H.sub.2-PVDC) (8.60 mg, 0.020 mmol) in DMF (0.4 mL) was
added to a solution of Yb(NO.sub.3).sub.3.5H.sub.2O (0.56 mg,
0.00125 mmol) in DMF (0.025 mL), Er(NO.sub.3).sub.3.5H.sub.2O (2.77
mg, 0.00625 mmol) in DMF (0.125 mL), and 1M HNO.sub.3(aq) (10.0
.mu.L) to produce a neon green solution. The vial was capped and
placed in a 100.degree. C. isotemp oven for 72 hours to produce
yellow crystalline needles. The crystals were collected, washed
with DMF (4.times.3 mL), and air dried (5.8 mg, 70.7%)
[0088] EA Calcd. (%) for
(Er.sub.0.81Yb.sub.0.19).sub.2(C.sub.26H.sub.20O.sub.6).sub.3(H.sub.2O).s-
ub.2.(DMF).sub.6(H.sub.2O).sub.5: C, 52.73; H, 5.35; N, 3.84.
Found: C, 52.87; H, 4.73; N, 4.35. FT-IR (KBr 4000-700 cm.sup.-1):
3399 (br), 2933 (w), 1656 (DMF C.dbd.O, m), 1602 (s), 1535 (s),
1416 (COO.sup.-, vs), 1259 (w), 1209 (s), 1180 (w), 1106 (w), 1043
(s), 962 (m), 865 (w), 779 (trans C.dbd.C--H, s), 709
cm.sup.-1(w).
[0089] Each framework is isomorphous with Yb-PVDC-1, as revealed by
comparison of their respective powder X-ray diffraction patterns.
The lanthanide composition in the products was determined by energy
dispersive X-ray spectroscopy (EDS) and directly correlates to the
amounts of each lanthanide salt used during synthesis (Table
1).
TABLE-US-00002 TABLE 1 Relative Ln.sup.3+ content for the
Er.sub.xYb.sub.1-x-PVDC-1 MOFs during synthesis (%.sub.Theo) and as
determined by EDS in the final product (%.sub.Act) PVDC
Er(NO.sub.3).sub.3 Yb(NO.sub.3).sub.3 %.sub.Theo Er.sup.3+
%.sub.Act Er.sup.3+ 1 0.02 0.00125 0.0025 33 .sup. 32 (.+-.2).sup.2
2 0.02 0.00375 0.0025 60 58 (.+-.2) 3 0.02 0.00625 0.0025 71 70
(.+-.2) 4 0.02 0.00625 0.00125 83 81 (.+-.3) .sup.aConcentrations
in mmol, .sup.berrors in parentheses
[0090] The EDS measurements were performed on a minimum of four
independently synthesized samples for each MOF and showed highly
reproducible results for each lanthanide composition. These results
indicate that any desired lanthanide composition can be produced in
a predictable fashion, simply by controlling the stoichiometry of
the reactants. The results also indicate that the MOF structure
does not preferentially include either lanthanide cation; hence,
any Er:Yb ratio can be targeted. This predictable aspect of the
synthesis is highly advantageous for a barcoded material, and in
this context it allows for the preparation of multiple barcodes
simply by varying the ratios of two emitters.
[0091] Photoluminescence studies were performed on each sample to
determine whether the different lanthanide compositions would
result in materials having unique and discernible barcoded signals.
MOFs 1-4 were suspended in chloroform and their excitation and
emission spectra were measured. The MOFs display both erbium and
ytterbium luminescence. The excitation spectrum of either the
erbium or ytterbium emission band contains two bands with maxima at
370 and 470 nm, similar to Yb-PVDC1. Excitation through either of
these bands simultaneously produces the characteristic Yb.sup.3+
emission band centered at 980 nm and the Er.sup.3+ band centered at
1530 nm in the NIR. As expected, increasing the amount of Er.sup.3+
and decreasing the amount of Yb.sup.3+ affected their respective
emission intensities by the same token. This demonstrates that, by
controlling lanthanide composition in keeping with the invention,
one can effectively control the resulting luminescence
intensities.
[0092] A plot of the ratio of the integrated intensities of the two
different lanthanides with respect to their atomic ratio reveals a
linear relationship. This trend is similar when either excitation
band is used and is reproducible across multiple samples. For
practical applications, this feature provides the option of using
two excitation sources for verifying an encryption tag.
Importantly, PXRD shows that these crystals maintain their
crystallinity throughout the important requirement for
applications.
[0093] Since the Er.sup.3+ and Yb.sup.3+ luminescence bands are in
the NIR range, they can not be seen by the naked eye. Therefore,
the signal can be monitored spectroscopically only, and the signal
intensities artificially correlated with two different visible
colors, for facile human observation. For example, purple could be
used to represent the Er.sup.3+ signal and green the Yb.sup.3+
signal. Their relative intensities also could be reflected in a
display. This would create four distinct barcodes correlating to
each MOF.
[0094] The number and diversity (i.e., the combination) of barcodes
can be increased, pursuant to the invention, by using more
metal:metal ratios or by incorporating additional lanthanides into
the material. To demonstrate this latter concept,
Er.sub.0.58Nd.sub.xxYb.sub.0.42-PVDC-1 (5) was prepared and, as
expected, it displayed a more complex barcode of NIR signals from
its three component lanthanide cations.
[0095] For practical applications, barcoded (marked) articles of
manufacture must be incorporated in ways that do not detrimentally
affect their signal. As a preliminary test to evaluate the
possibility of incorporating MOFs into actual materials, we coated
2 (Table 1) on a microscope slide with an adhesive, and then
investigated its luminescence properties. Upon excitation at 490 nm
the Yb.sup.3+/Er.sup.3+ barcode (mark) was easily detected in the
NIR range.
[0096] Marking an article of manufacture with a MOF can be effected
via various technologies, including but not limited to conventional
printing, spin coating, safety threads and adhesion to an article
of manufacture.
[0097] The MOF formulation selected is dependent on the marking
technology used. Solid as well as and viscous liquid formulations,
are employed in a number of marking technologies, depending on the
material being marked. The MOF is prepared, isolated in crystal
form in the conventional manner, and then dried. Formulation of the
MOF is achieved by dissolving the complex in a suitable organic or
aqueous solution. Organic solvent in this case includes alcohol,
amine, ether aromatic, alkane and alkene or a mixtures therein.
Aqueous solution in this case denotes acidic to basic pH solutions
prepared from known acids and bases. Solutions can then be
concentrated to a viscous liquid or an emulsion prior to the
application process of choice. Alternatively, formulation can
achieved by combining the viscous liquid with a binder such as
acrylic polyamide, polyurethane, polyester, polyethylene or an
adhesive. The marking technology employed is discussed in detail
below, which as mentioned employs a specifically tailored
formulation.
[0098] Marking an article of manufacture with a MOF in a dried
crystalline state can be accomplished by coating the MOF with an
adhesive to secure the MOF to the article of manufacture.
Alternatively, the dried crystalline MOF can be deposited in a
clear tube or similar small clear container, and secured to the
article of manufacture with an adhesive. Emulsions of the MOF are
used to mark items such as safety threads, which is then
incorporated into an identity card, bank note, check or currency.
Furthermore, an organic viscous liquid form of the MOF is combined
with a binder and used for spin coating a polymer film or fiber.
The aqueous or organic viscous liquid form of the MOF is used in a
conventional printing system, to mark an article of manufacture.
Lastly, a viscous liquid form of the MOF is smeared with a tool or
device on an article of manufacture and then coated with an
adhesive.
TABLE-US-00003 TABLE 2 Polydentate triphenylene-functionalized
complexes.sup.1 Lanthanide Ligand solvent t (.mu.s) Yb terphenyl
(1) DMSO 9.1 Yb triphenylene (2) DMSO 9.4 ##STR00005## ##STR00006##
Schematical representation of the terphenyl-based complex (1)Ln and
its triphenylene-functionalized derivative (2)Ln
TABLE-US-00004 TABLE 3 Pyrene sensitizers.sup.2 Ligand solvent t
(.mu.s) Yb [L1YbL2]- water 0.72 Yb YbL3 water 0.74 Yb YbL4 water
1.34 ##STR00007## ##STR00008## ##STR00009## ##STR00010## Structures
of Ligands
TABLE-US-00005 TABLE 4 Dye sensitizers.sup.3 Ligand solvent t
(.mu.s) Yb H4(fluorescein) Methanol 9.8 Yb Br4(eosin) Methanol 11.6
Yb I4(erythrosin) Methanol 10.2 Yb Fluoreson Methanol 2.47
##STR00011## ##STR00012## ##STR00013## Terphenyl complexes
functionalized with fluorescein, eosin, and erythrosin
TABLE-US-00006 TABLE 5 Poly(pyrazolyl)borate ligands.sup.4 Ligand
solvent t (.mu.s) Yb [Yb(L1)(NO3)2] methanol 1.58 Yb [Yb(L2)(NO3)]
methanol 0.45, 1.36 Yb [Yb(L1)(dpm)2] methanol 2.94 Yb
[Yb(L1)2][BPh4] methanol 2.01 ##STR00014## ##STR00015##
TABLE-US-00007 TABLE 6 Podates.sup.5 Ligand solvent t (.mu.s) Yb
[YbH2Tsox].sup.3- water 2.21(1) Yb [YbH2TsoxMe].sup.3- water
5.79(1) Yb [YbH2Tsox].sup.3- & Triton X-100 water 2.82(1) Yb
[YbH2TsoxMe].sup.3- water 6.42(3) ##STR00016##
TABLE-US-00008 TABLE 7 Lehn cryptand.sup.6 Lanthanide solvent t
(.mu.s) Yb Lehn Cryptand water 0.52 ##STR00017## Synthesis of
L.sup.1 and its complexes
TABLE-US-00009 TABLE 8 Poly(pyrazolyl)borate and 1,3-diketonate
ligands.sup.7 Lanthanide Ligand solvent t-H (.mu.s) Yb
[M(L2)(dbm)2] CH2Cl2 11.2 Yb [M(L2)(dbm)2] CH3OH 8.95, 1.27
##STR00018## ##STR00019##
TABLE-US-00010 TABLE 9 Porphyrins.sup.8 Lanthanide Ligand solvent
t-H (.mu.s) Yb P1 CH3OH 4.8 Yb P2 CH3OH 7.8 Yb P3 CH3OH 8.2 Yb P4
CH3OH 12.1 Yb P5 CH3OH 1.7 Yb P6 CH3OH 1.1 Yb P7 CH3OH 0.9 Yb P8
CH3OH 0.9 Yb P9 CH3OH 1.1 Yb P10 CH3OH 2.1 Yb P11 CH3OH 2.3 Yb P12
CH3OH 5.6 ##STR00020## ##STR00021## ##STR00022## ##STR00023##
##STR00024## P.sub.5: R.sup.1 = R.sup.2 = R.sup.3 = R.sup.4 =
C.sub.2H.sub.5 P.sub.6: R.sup.1 = R.sup.2 = R.sup.3 = R.sup.4 =
C.sub.3H.sub.7 P.sub.7: R.sup.1 = R.sup.2 = R.sup.3 = R.sup.4 =
C.sub.4H.sub.9 P.sub.8: R.sup.1 = R.sup.2 = R.sup.3 = R.sup.4 =
C.sub.9H.sub.19 ##STR00025## ##STR00026## ##STR00027## ##STR00028##
indicates data missing or illegible when filed
* * * * *